How to create a seamlessly looping ocean
From Haunt's trick bag:



&nbsp;&nbsp;Instead of using one Ocean Modifier, use two identical ones. The following values are the ones used in this example.

Key Frames on frame 1 and frame 21. Since these frames will be identical, the loop will only include frames 1 to 20.

First Ocean Modifier: 


Animate the time from 15 to 20
Animate the scale from 0.0 to 3.0


Second Ocean Modifier:


Animate the time from 20 to 25
Animate the scale from 3.0 to 0.0


&nbsp;&nbsp;Since both Modifiers are identical, one starts exactly with the shape the other one ends with. And the scale is used to blend between them. 


Set the interpolation in the F-graph Editor to Linear (T) to get a constant motion. 
The Geometry of the second modifier must be set to Displace, to avoid overwriting the first.